check the regs, but I dont believe something like that will qualify him for Disability.
With that said, if he is unable to maneuver natural terrain with out the aid of a prosthesis, like cane or crutch, then he would probably qualify
A buddy of mine's dad was able to get a disabled hunters placard when he was going through kemo treatment. He was unable to walk with out the aid of a cane or walking stick of some sort.